Tuned transformer assembly



V. P. FRIBERG TUNED TRANSFORMER ASSEMBLY April 13, 1954 Filed Sept. 11, 1951 2: Sheets-Sheet l INVENTOR. VmcEN'rP FRIBEIIEG. BY

ATTOIFNEKF.

g l g6 April 13, 1954 v. P. FRIBERG TUNED TRANSFORMER ASSEMBLY 2 Sheets-Sheet 2 Filed Sept. 11 1951 INVENTOR. VINCENTP FRIBERG.

ATTORNEVJ Patented Apr. 13, 1954 TUNED TRANSFORMER AS SEMBLY Vincent P. Friberg, Lyndhurst, N. J assig-nor to Automatic Manufacturing Corporation, Newark, N. J., a corporation of New Jersey Applicationseptember 11, 1951, Serial No. 246,079

v 11 Claims. 1

This invention pertains to tuned, high frequency transformer assemblies and more particularly to transformers of this type which are especially adapted for use in the intermediate frequency portion of superheterodyne radio re ceivers and which are commonly referred to as I. F. transformers.

Intermediate frequency, or I. R, transformer assemblies, in general, comprise a pair of magnetically coupled coils, constituting primary and secondary transformer windings, and tuning capacities connected in shunt with the coils. The transformers may be tuned either by variation of the shunt capacities or by magnetic cores associated with the coils or by a combination. of both.

. If magnetic cores are employed to permit adjustment of the tuning of the transformer (inductance tuning), small, fixed capacities are normally connected in shunt with the coils because they stabilize the transformer tuning.

To provide a close control over the frequency to which an I. F. transformer is tuned, the coils and their associated capacities are generally assembled as a unit. Such an assembly is practically necessary for transformers designed to operate at very high radio frequencies at which lead lengths and the relative positions of the components have a substantial effect on the frequency to which the transformers tune.

It is desirable to reduce the size of an I, F.

transformer assembly to a minimum, and it is generally desirable to reduce the cost of a transformer assembly such as by simplifying its assembly by using inexpensive parts. The size can be reduced by reducing the size of the coils which in turn can be accomplished by the use of mag- The shells and cores increase the inductance of a given size of coil, and the use of adjustable cores eliminates the need for further adjustable devices for tuning the transformer assembly. Furthermore, the cores extend the high permeability path of the shells and hence reduce the length. of the low permeability air path.

In accordance With the preferred embodiment of my invention, a pair of transformer coils is enclosed by a pair of magnetic shell members having abutting surfaces so oriented as to lie in a plane which is substantially parallel to the common magnetic axis of the coils. With this arrangement air gaps in the shell members which are transverse to the magnetic lines produced by thecoils are avoided, and, hence, the inductance for a given size of coil may be a maximum.

The transformer assembly of my invention 2 preferably also includes magnetic cores which are insertable in the coils and which are mounted between the adjacent surfaces of the shell members so as to extend the high permeability path of the shell members into the coils without the addition of a further air gap. The coils are preferably mounted on a coil form which is substantially enclosed by the shell members and the coil form has an aperture therein. The coils, the coil form, and the shell members are held in their proper positions by a pin which is engaged by the shell members and which extends through the aperture in the coil form.

A condenser unit is mounted against the side of one of the shell members, and preferably the above-mentioned pin forms a part of the condenser unit and extends substantially perpendicular to a side thereof. The pin may also serve to maintain the parts of the condenser unit in their proper positions.

The shell members and the condenser unit are held together by means of the combined action of a resilient clamp and a shield can which encloses at least a portion of the clamp and which substantially encloses the shell members and the condenser unit.

An object of my invention is to provide a tuned transformer assembly which is small in size, easy to assemble, and economical to manufacture. A tuned transformer assembly constructed in accordance with my invention may have a volume of the order of cubic inch, and may therefore be much smaller than prior art transformer assemblies operating at the same frequency.

Other objects and advantages of the invention will more fully appear from the following detailed description setting forth the manner in which I now prefer to practice the invention and from the accompanying drawings in which:

Fig. 1 is an electrical circuit diagram of the tuned transformer assembly of my invention;

Fig. 2 is a perspective view of the preferred embodiment of my invention;

Fig. 3 is a perspective view of the embodiment shown in Fig. 2 with the shield can and the clamping member removed from the remainder of the assembly;

Fig. 4 is a cross-sectional, side elevation, enlarged view of the embodiment of the invention shown inFigs. 2 and 3;

Fig. 5 is a cross-sectional, end elevation view of the embodiment shown in Fig. .4;

Fig. 6 is a cross-sectional, bottom view of the embodiment shown in Fig. 4 and taken along the line '65 indicated in Fig. 4

' and the coil form I3 being cylindrical.

, the coils I and 2.

Fig. 7 is an exploded perspective view of the components included in the preferred embodiment of my invention; and

Fig. 8 is a fragmentary, side elevation view of a modification of the invention.

Referring to the circuit diagram of Fig. 1, it will be seen that the I. F. transformer assembly of the invention includes a pair of coils I and 2 which are magnetically coupled and whose inductance is adjustable by means of magnetic cores 3 and 4. The coils I and 2 and the cores 3 and 4 are enclosed by shell members 5 and 8 of magnetic material. Fixed condensers I and 8 are connected in shunt with the coils I and 2, respectively, and the coils may be connected to vacuum tubes or other devices by means of terminals 9-I 2.

Referring to Figs. 2 through 7 and particularly to Figs. 4 through '7, it will be seen that the coils I and 2 preferably are mounted on a coil form I3, the coils being annular in the embodiment shown When the coils are so constructed and mounted, the magnetic axis of the coils is substantially the same as the axis of the cylindrical coil form. The coil form I3 has an aperture I4 therein for purposes hereinafter described.

To permit adjustment of the inductance of the coils I and 2 and also to increase their inductance, cores 3 and 4 are inserted within the ends of the coil form I3 and are insertable within the coils I and 2. The cores 3 and 4 may be adjusted axially of the coil form I3 by means of a screw driver inserted into their slotted heads, the cores being threaded externally as shown and engaging the inner walls of the coil form which preferably have threads thereon. The cores are made of magnetic material and preferably are made of powdered iron admixed with a, suitable powdered filler, such as a thermo-setting resin, and molded into the configuration shown under heat and pressure. The cores 3 and 4 are held in their adjusted positions by virtue of the friction between them and the inner wall of the coil form I3, the friction preferably being increased over its normal value by the pressure applied to the 7 ends of the coil form I3 by the shell members 5 and 5.

The coils I and 2 are enclosed by the shell members 5 and 5 which are also made of magnetic material and preferably of powdered iron molded in the same manner as the cores 3 and l. Each of the cores 5 and 6 has a semi-cylindrical cavity therein, the cavity I5 in shell member 5 being shown in Fig. '7, and when the two shell members 5 and 6 are assembled about the coils I and 2 with their surfaces I1 and I8 in abutting relationship, the two shell members 5 and 5 form a substantially cylindrical cavity in which the coils I and 2 are contained.

Each of the shell members 5 and 6 also has therein semi-circular cut-out portions I9, 20, 2I and 22 which when the shell members 5 and 5 are placed in abutting relationship preferably grip the ends of the coil form I3 as described above.

When the shell members 5 and 6 are assembled as shown, there is substantially no air gap which is transverse to the magnetic lines produced by Furthermore, the air path out side of the shell members 5 and 6 is further reduced by the cores 3 and 4 which serve to extend the high permeability magnetic path. The length of the air path may'befurther reduced by terminating the coil form I3 at the inside walls bly of the shell members 5 and 5 with the coil form I3 and'the associated coils I and 2, the shell members 5 and 5 and the coil form I3 may be held in their proper positions by means of a pin such as the pin 25 inserted through these apertures. Also, after the shell members and the coil form are in their assembled positions, the pin 25will serve to hold these components in their proper relationships.

Although the pin may be a separate pin,

' it is preferably secured to a side of a condenser unit mounted against one of the shell members 5 and 5. Also, in the preferred form, the pin 25 serves to hold the elements of the condenser unit in their proper positions. As illustrated in the drawings, the pin 25 is formed integrally with or is cemented to an insulating plate 25 having recesses 21 and 28 therein for receiving and holding the terminals 9-I2 therein. The condenser unit also comprises an insulating plate 29 such as a plate of mica having on both sides thereof metallic coatings such as coatings 30 and 3| which may be coatings of silver, for example. These coatings 30, 3|, etc., form the plates of the condenser unit and are connected to the coils I and 2 by means of terminals 5-I2 which are in contact with the coatings when the condenser unit is assembled.

The condenser unit also comprises an insulating plate 32 which serves to insulate the terminals 9 and II from the shell member 5 when the transformer unit is assembled. The insulating plates 29 and 32 have apertures 33 and 34 therein through which the pin 25 passes. Also, when the pin 25 is cemented to the insulating plate 26, the insulating plate 25 preferably has an aperture therein into which the pin 25 fitsand in which the end of the pin 25 is cemented.

After the shell members, the coil unit and the condenser unit are assembled, a resilient clamping member 35, preferably having a c-shape as shown in the drawings, is placed over the assembled components. The resilient clamping member 35 has a first portion 36 which engages the side of the shell member 6 having the aperture 24 therein and a second portion 31 which engages the side of the insulating plate 26. The clamping member 35 is preferably made of thin sheet metal and may have insufficient stiffness to hold the assembled components by itself, but the portion 31 is bowed and when the clamping member 35 and the assembled shell members and con- I denser unit are inserted within a shield can 33,

the bowed portion 31 applies sufficient force to the side of the insulating plate 25 to hold the condenser unit tightly against the side of the shell member 5 and to press the surface ll of the shell member 5 against the surface I3 of the shell member 5. The clamping member 35 also has an aperture 39 therein to permit insertion of an adjusting tool therethrough and adjustment of i the core 4.

-tially encloses the shell members and the condenser unit. The shield can 38 is preferably made of metal and is not necessarily made of magnetic material because adequate magnetic shielding of the coils I and 2 may be provided by the shell members 5 and 6. The shield can 38 has an aperture 40 therein which is sufficiently large to permit passage of the terminals 9 through I2 therethrough without touching and has an aperture 4| therein to permit passage of an adjusting tool therethrough for the purpose of adjusting the shield can 38.

Thus, the transformer assembly of my invention may be very small in size because the major portion of the magnetic path has a high permeability and the length of the air gap transverse to the magnetic line is reduced to a small value. Furthermore, a small number of parts are required and several of the parts are interdependent so as to avoid unnecessary duplication of parts.

Transformer assemblies constructed in accordance with the invention have been found to have the desired magnetic coupling between the coils I and 2 with the construction shown. However, if it is desired to reduce the coupling between the coils I and 2, it may be reduced by the addition of a wall of magnetic material within the cylindrical cavity between the shell members 5 and 6 and intermediate the coils I and 2. Such a wall may be relatively thin and extends in a plane substantially perpendicular to the magnetic axis of the coils I and 2.

Having thus describedmy invention with'particular reference to the preferred form thereof and having shown and described certain modifications, it will be obvious to those skilled in the art to which the invention pertains, after understanding my invention, that various changes and other modification may be made therein without departing from the spirit and scope of my invention, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A tuned transformer assembly comprising a coil form having a longitudinal axis and having an aperture therein facing in a direction transverse to said axis; a pin extending through said aperture in said form and transversely of said axis; a coil mounted on said form around said axis; and a pair of magnetic shell members enclosing said coil, said shell members being mounted in engagement with said pin.

2. A tuned transformer assembly comprising a coil form having a longtiudinal axis and having an aperture therein facing in a direction transverse to said axis; a pair of coils mounted on said form around said axis; a pair of magnetic shell alignment withthe aperture of the other memher in a direction transverse to said axis and in,

alignment with the aperture in said form; and

a pin extending transversely .of said axis and through said aperture in said shell members and said form.

3. A tuned transformer assembly comprising a coil form having a longitudinal axi and having an aperture therein facing in a direction transverse to said axis; a pair of coils mounted on said form, said coils when energized being adapted to produce a magnetic field extending in a predetermined direction; a pair of magnetic shell members mounted in abutting relationship and enclosing said coils, said shell members abutting each other in a plane which is substantially parallel to said predetermined direction and each having apertures in the sides thereof, the aperture in one member being in alignment with the aperture in the other member in a direction transverse to said axis and in alignment with the aperture in said form; and a pin extending transversely of said axis through said apertures in said members and said form.

4. A tuned transformer assembly comprising a coil form having a longitudinal axis and having an aperture therein facing in a direction transverse to said axis; a pair of coils mounted on said form, said coils when energized being adapted to produce a magnetic field extending in a predetermined direction; a pair of magnetic shell members mounted in abutting relationship and enclosing said coils, said shell member abutting each other in a plane which is substantially parallel to said predetermined direction and providing substantially continuous magnetic walls on all sides of said coils and each member having an aperture in the side thereof, the aperture in one member being in alignment with the aperture in the other member in a direction transverse to said axis and in alignment with the aperture in said form; a pair of magnetic cores mounted between adjacent surfaces of said shell members and insertable in said coils, each of said cores being adjustable in a direction substantially parallel to said plane; and a pin extending transversely of said axi through said apertures in said shell members and said form.

5. A tuned transformer assembly comprising a coil form having a longitudinal axis and having an aperture therein facing in a direction transverse to said axis; a pair of coils mounted on said form, said coil when energized being adapted to produce a magnetic field extending in a predetermined direction; a pair of magnetic shell members mounted in abutting relationship and enclosing said coils, said shell members abutting each other in a plane which is substantially parallel to said predetermined direction and providing substantially continuous magnetic walls on all sides of said coils and each member having an aperture in the side thereof, the aperture in one member being in alignment with the aperture in the other member in a direction transverse to said axis and in alignment with the aperture in said form; a pair of magnetic cores mounted between adjacent surfaces of said shell members and insertable in said coils, each of said cores being adjustable in a direction substantially parallel to said plane; a pin extending transversely of said axis through said apertures in said shell members and said form; a shield can substantially enclosing said shell members; and a resilient member compressed between said shield can and said shell members.

6. A tuned transformer assembly comprising a coil form having a longitudinal axis and having an aperture therein facing in a direction transverse to said axis; a pair of coils mounted on said form, said coils when energized being adapted to produce a magnetic field extending in a predetermined direction; a pair of magnetic cores each insertable within one of said coils; a pair I of magnetic shell members mounted in abutting relationship and enclosing said coils, said shell membersabutting each other in a plane which is substantially parallel to said predetermined direction and providing substantially continuous magnetic'walls on all sides of said coils and each member having an aperture in the side thereof, the aperture in one member being in alignment with the aperture in the other member in a direction transverse to said axis and in alignment with the aperture in said form; a pin extending transversely of said axis through said apertures in said shell members and said form; a shield can substantially enclosing said shell members; and

a resilient member compressed between said shield can and said shell members.

7. A tuned transformer assembly comprising a coil form having an aperture therein, a pair of coils mounted co-axially on said form, a pair of magnetic coreseach insertable within one of said coils; a pair of magnetic shell members mounted in abutting relationship and enclosing said coils,

said shell members abutting each other in a plane which is substantially parallel to the axis of said coils and each having apertures in the sides thereof, the aperture in one member being in alignment with the aperture in the other memher and with the aperture in said form; a condenser unit comprising condenser plates and a .pin extending from a side of said .unit, said unit being mounted against the side of-one of-said shell members with said pin extending through said apertures in said shell members and said form; conductive means connecting said condenser plates to said coils; a shield can substantially enclosing said shell members and said condenser unit; and a resilient member mounted between said shield can and the enclosed shell members and condenser unit.

8. A tuned transformer assembly comprising a coil form; a pair of coils encircling said form and spaced from each other axially of said form,

- said form having an aperture therein, intermediate said coils; a pair of ferromagnetic cores r mounted co-axially with said form and adjustable axially with respect thereto, each of said cores being insertable within one of said coils;

. a pair of ferromagnetic shell members mounted in abutting relationship and enclosing said coils, said shell members abutting each other in a' plane which is substantially parallel to-the axis of said form and each having apertures in the sides thereof, the apertures in one member being in alignment with the aperture in the other member and with the aperture in said form; a concoil form; a pair of coil encircling said form and spaced from each other axially of said form, .saicl-form having an aperture therein interme-.

'8 diate said coils; a pair of ferromagnetic cores mounted co-axially with said form and adjustable axially with respect thereto, each of-said cores being insertable within one of said coils; a pair of ferromagnetic shell member mounted in abutting relationship and enclosing said coils, said shell members abutting each other in a. plane which is substantially parallel to the axis of said form and each having apertures in the sides thereof, the aperture in one member being in alignment with the aperture in the other member and with the aperture in said form; a condenser unit comprising three plates of insulating material each having an aperture therein, said plates being mounted with the apertures therein in alignment with each other and with the apertures in said shell members and said form and with one plate intermediate the others, a first; pair of condenser plates mounted between said one plate and a second one of said three plates and a' second pair of condenser plates mounted between said one plate and a third one of said threeplates; conductive means connecting said condenser plates to respective ones of said coils; a pin extending through said apertures in said insulating plates, said shell members and said form; a C-shaped, resilient clamping member mounted with one portion thereof in engagement with one side of said condenser unit and an opposite portion thereof in engagement with said side of said other shell member having an aperture therein; and a shield can substantially enclosing said shell members and said condenser unit and adapted to press said portions of said clamping member into tight engagement with said shell members and said condenser unit.

, 10. A tuned transformer assembly comprising a coil form; a pair of coils encircling said form and spaced from each other axially of said form,

said form having an aperture therein intermediate said coils; a pair of ferromagnetic cores mounted co-axially with said form and adjust- I able axially with respect thereto, each of said cores being insertable within one of said coils; a pair of ferromagnetic shell members mounted in abutting relationship and enclosing said coils, said shell members abutting each other in a plane which is substantially parallel to the axis of said form and each having an aperture in a side thereof and the apertures in one member being in alignment with the aperture in the other memher and with the aperture in said form; a condenser unit comprising a first plate of insulating 'material having an aperture therein, a second plate of insulating material mounted beside said ,.first plate and having an aperture therein in alignment with the aperture in said first plate, a pair of condenser plates mounted on each side of said second plate, said condenser plates being insulated from each other, a third plate of insulating material mounted beside said second plate on the side thereof opposite from said first plate. conductive terminals connected to said condenser plates extending beyond an edge of said second plate, and a pin secured to said third plate and extending substantially perpendicular thereto and through said apertures in said first and second plates, said unit being mounted with. said first plate against one of said shell members with said pin extending through said apertures in said shell members and said form; means connecting said terminals to respective ones of said coils; a C- ,shaped, resilient clamping member mounted 7 'with' one portion thereof engagement with the side of said third plate remote from said second plate and an opposite portion thereof in engagement with said side of said other shell member having an aperture therein, at least one of said last-mentioned portions being bowed in its free state; and a shield can substantially enclosing said shell members, said condenser unit and said portions of said clamping member and having an aperture therein permitting passage of said terminals therethrough, said portions of said clamping member also engaging the inner wall of said can with said bowed portion resiliently pressing thereagainst.

11. A tuned transformer assembly comprising a coil form; a pair of coils encirclin said form and spaced from each other axially of said form, said form having an aperture therein intermediate said coils; a pair of ferromagnetic cores mounted co-axially with said form and adjustable axially with respect thereto, each of said cores being insertable within one of said coils; a pair of ferromagnetic shell members mounted in abutting relationship and enclosing said coils, said shell members abutting each other in a plane which is substantially parallel to the axis of said form and each having an aperture in a side thereof, the aperture in one member being in alignment with the aperture in the other member and with the aperture in said form; a condenser unit comprising a first plate of insulating material having an aperture therein, a second plate of insulating material mounted beside said first plate and having an aperture therein in alignment with the aperture in said first plate, said second plate having a pair of conducting coatings on both sides thereof, said coatings being insulated from each other and each coating on one side thereof being substantially co-extensive with a coating on the opposite side thereof, a third plate of insulating material mounted beside said second plate on the side thereof opposite from said first plate, four conductive terminals each having contacting and connecting portions, two of said terminals being mounted between said first and second plates and two of said terminals being mounted between said second and third plates and said terminals having the contacting portions thereof in contact with the coatings on the adjacent sides of said second plate and all having the connecting portions thereof extending beyond adjacent edges of said plates, said third plate having recesses therein for holding said terminals in predetermined positions, and a pin secured to said third plate and extending substantially perpendicular thereto and through said apertures in said first and second plates, said unit being mounted with said first plate against one of said shell members with said pin extending through said apertures in said shell members and said form; means connecting said terminals to the respective ends of said coils; a C-shaped, resilient clamping member mounted with one portion thereof in engagement with the side of said third plate remote from said second plate and an opposite portion thereof in engagement with said side of said other shell member having an aperture therein, at least one of said last-mentioned portions being bowed in its free state; and a shield can substantially enclosing said shell members, said condenser unit and said portions of said clamping member and having an aperture therein adjacent one end of i said form and a further aperture in a side thereof permitting passage of said terminals therethrough, said portions of said clamping member also engaging the inner wall of said can with said bowed portion resiliently pressing thereagainst.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,283,924 Harvey May 26, 1942 2,430,990 Moore Nov. 18, 194.7 2,435,630 Ketcham Feb. 10, 1948 2,483,919 Mazzola Oct. 4, 1949 FOREIGN PATENTS Number Country Date 125,910 Australia Oct. 23, 1947 436,808 Great Britain Oct. 18. 1935 

